Information, Tips and tricks, schematics and How to... for Otari MTR 90 recorders

   
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The Otari MTR 90 mkII is a great Tape Recorder...
The Transport is good, the audio sounds great, and she does not require
much Technical Service and any needed repairs are somewhat easy to do... for a tech that is!
 
If you own one, here is a basic DAILY check you need to make BEFORE you use the machine.

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1) Check Tension Arms for wobble or looseness
             Just wiggle the tension rollers by hand, they should be firm...

2) Check Upper and Lower LED functions
             Move tension rollers all the way up and then down. Leds should go
             on and off about 1/4 inch from top and bottom

3) Check tape tensions physically on tape near Tension arms
             Test by finger 'feel'... tape at top and bottom should 'feel' about the same.

  Details below....

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1)First you need to learn the 'feel' of the Tension Arms.
They should NOT rock back and forth sideways, they should 'feel' solid.

ANY movement sideways, or the Tension Arms feeling 'loose' indicates
the lower screw is coming undone, and you run the risk of serverly
mis-set tensions.

You MUST try and tighten the lower bolt in the Tension Arm -
WITHOUT CHANGING THE POSITION OF THE ARM ITSELF.
Drop the VU Meter Pannel and you can get access to the lower bolt
Which you can access through a hole in the Deck Plate very close to the Tension Arm.

2)Next you must move each tension arm by hand from the lowest position to the top.
Note that at the Lowest position there is a LED on the Tension Control Card which
should be 'On'.   Raising the Tension Arm Slowly, this LED should go 'OFF' about
a 1/4 inch above the lowest point.   As you move the Tension arm upwards,
another LED should go 'On' about 1/4 inch from the very top of the Tension Arm's Travel.
The Upper LED should go 'OFF' when lowering the Tension arm, about 1/4 inch from the top.
Check EACH Tension Arm.     The Tension system needs to known when the arm
is at it's bottom and at it's top.     You should check this EVERY DAY !!

3)Load some good but 'scrap' tape on the machine, and go into a FAST WIND mode.
                                Do NOT use a session tape for this test !!!!!

IN a well running machine, the physical tension on the tape itself is
  EQUAL at the top of the tape and the bottom of the tape.
This indicates the physical alignment of the Tension Arms is correct.

Ever so slightly and carefully, bring a finger in and just LIGHTLY 'feel' the top and bottom of the tape
on the outside of the Tension Arm (towards the reel) about 3/4 inch from the Tension Arm
and from the outside of the deck.       Just use a VERY slight finger pressure.
  -   the 'feel' of the tape tension should be the same, or very close, at top and bottom.
                        Check BOTH Tension arms.

If the tensions are severly different at the top and bottom
You likely will see the tape sort of 'wobbling' back and forth in the wind modes
where the tape tension is weakest.

With SEVERLY different tape tensions between the top and bottom of the tape,
you will likely have to hire a good experienced tech to come in and
PHYSICALLY align the Tension Arms.

NEVER TRY TO PHYSICALLY ALIGN THE TENSION ARMS YOURSELF !!!
    AND NEVER TRY AND BEND THE TENSION ARMS !!
        Correct Physical Re-Alignment of the Tension Arms is very difficult to do...
                                AND IS NEVER DONE BY BENDING THE ARMS   !!!!

NOTE:     Athan sells new and better designed Tension Arm assemblies that improve the functioning
of the Tension Arms and help prevent physical mis-alignment... well worth the cost of them!

Athan MTR 90 Parts Page

 

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RECAP:
1) Check Tension Arms for wobble or looseness

2) Check Upper and Lower LED functions

3) Check tape tensions physically on tape near Tension arms

 

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